Tonsillectomy is the most frequently performed operation in the United States; about 1,000,000 children are subjected to this procedure annually. Yet, for at least 50 years, widely divergent attitudes and practices have been maintained concerning the indications for tonsillectomy and adenoidectomy. Important among the reasons for this unsatisfactory situation are the facts that (a) few actual studies of indications have been carried out, and (b) those few studies contain substantial limitations, or flaws in experimental design, or both. Quite apart from considerations of real or theoretical risks of tonsil-adenoid surgery, there exists at present no body of reliable data from which to estimate either the efficacy of surgery or the likelihood of spontaneous improvement in many conditions attributed to tonsil or adenoid disease. The objective of this research is to arrive at rational indications for tonsillectomy and for adenoidectomy, based on the outcome of a prospective, controlled, clinical trial. A subsidiary objective is to explore possible effects of removing tonsils or adenoids on certain presumed measures of immunologic competence. All patients referred from practicing physicians or from out-patient clinics of the Children's Hospital for consideration of tonsil or adenoid surgery are seen in a special T & A Evaluation Clinic, where they receive detailed, standardized evaluation. From among this group, potential candidates for adenoidectomy, or tonsillectomy, or both, are identified on the basis of stringent indications for each procedure. These selected children are then randomly divided into surgical and control groups, subject to informed parental consent. Their clinical courses thereafter are compared with those of patients not considered appropriate candidates for surgery. Differences, if any, among the three groups in various parameters of health and disability will be measured.